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Petunias (Petunia spp.) come in several varieties with different growth habits. Most are grown as annuals, although they are perennial in U.S. Department of Agriculture plant hardiness zones 10 and 11. Multiflora varieties produce large single or double flowers, while multiflora types feature a profusion of small blooms. Milliflora petunias produce small flowers on dwarf plantw, while the spreading or Wave petunias act as ground covers.

Site Conditions

The right soil and sun encourage healthy petunia growth. Petunias tolerate most well-drained soils, but you can work in a 2-inch layer of compost before planting to improve moisture and nutrient qualities in the bed. They flower best with a full six to eight hours of sun a day, although they can tolerate some afternoon shade with only a slight reduction in blooms. Petunias also grow well in containers and hanging baskets when you plant them in high-quality potting soil and place them in the sun.

Germination

Sowing from seed keeps the cost of petunias down, buy you can also buy plants at the garden center. The seeds germinate within one week when sown 1/4 inch deep in moist potting soil indoors or outside. The soil temperature should be between 65 and 75 degrees Fahrenheit for good germination. The plants quickly grow and can begin producing flower buds in as little as six to eight weeks. Starting the seeds indoors six weeks before the last expected frost in your area gives you ready-to-bloom plants soon after transplanting.

Basic Care

Healthy petunia growth depends on regular watering. The soil should stay evenly moist without becoming soggy. Garden plants usually need about 1 inch of water weekly, or enough so the soil doesn't dry out beyond its top 1 inch. Potted petunias may need daily watering if the top 1 inch of soil dries. A soluble fertilizer, such as a 10-10-10 blend, applied monthly at the package-recommended rate for garden plants, or every two weeks for potted plants, provides nutrition for continued healthy growth.

Pruning

Flower and bud growth depend on proper planting and care, along with some light pruning. Petunias tend to become leggy as the season progresses. Shearing back the top of the plants by one-half their height forces a new flush of growth and branching, which results in more buds. Trimming off the dead flowers as soon as they wilt also increases flowering because the petunias won't set seed and complete their life cycle. You can cut back petunias at any time to encourage more flowering or if the plants look weak and spindly.

About the Author

Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.